1. Field of Application
The present invention relates to a preceding vehicle selection apparatus. The apparatus is installed in a host vehicle and serves to select another vehicle which is running directly ahead of the host vehicle, in the same travel path.
2. Description of Related Art
Types of vehicle-installation apparatus are known for use in recognizing obstacles located in the surroundings of the vehicle (host vehicle) in which the apparatus is installed, and in particular for selecting an obstacle which is a preceding vehicle. The term “selecting a preceding vehicle” as used herein signifies detecting (recognizing) a vehicle which is located immediately ahead of the host vehicle and is running in the same travel path (i.e., the same traffic lane) as the host vehicle. The operation is based on transmitting waves (light waves, millimeter-band electromagnetic waves, etc.) into a region ahead of the host vehicle, detecting resultant reflected waves from any obstacles, and selecting a preceding vehicle from the detected obstacles. Such an apparatus is described for example in Japanese patent publication No. 2001-283391, designated in the following as reference document 1. The results obtained from such an apparatus may be used in controlling the running speed of the host vehicle, by control of acceleration and deceleration, to maintain a required separation distance from the preceding vehicle. Such a function is referred to herein as “vehicle following control”.
Reference document 1 also describes a method of calculating a probability referred to in the following as the “host vehicle path probability”. This is the estimated probability that, when another vehicle has been detected, it is moving along the same travel path as the host vehicle. Values of host vehicle path probability are calculated at successive points in time, each calculation based upon the detected position of the other vehicle relative to the host vehicle and the estimated curvature of the travel path of the host vehicle at that time.
The curvature of the travel path of the host vehicle is estimated based on the yaw rate and running speed of the host vehicle. Another vehicle is selected as being a preceding vehicle so long as the host vehicle path probability obtained for that vehicle is above a predetermined threshold value.
However in some cases the yaw rate may fluctuate in an unstable manner, e.g., due to irregularities (bumps and hollows) in the road surface or variations in the shape of the road, or due to effects of behavior of other vehicles on the driver of the host vehicle, etc., causing steering operations by the driver to rapidly vary the steering angle in an unstable manner. Such rapid variations in the yaw rate correspond to sudden changes in the heading direction of the vehicle alternately to the right side and to the left side, which are unrelated to the required (intended) travel path. As a result of the fluctuations in yaw rate, the estimated travel path of the host vehicle (i.e., as indicated by successively obtained values of curvature of the travel path, calculated based on detected values of the yaw rate and running speed) will become unstable. The selection of a preceding vehicle may thereby be erroneously cancelled, or a vehicle which is driving in an adjacent traffic lane to that of the host vehicle may be erroneously selected as a preceding vehicle.
In such cases, control operations by the preceding vehicle selection apparatus for implementing the vehicle following control may cause unexpected variations in acceleration and deceleration of the host vehicle, i.e., variations which are not intended by the driver, causing feelings of anxiety in the driver.
It is known to apply filtering to the successively calculated values of host vehicle path probability, and utilize the resultant filtered values in estimating the travel path of the host vehicle. This is intended to suppress the effects of such fluctuations in the yaw rate. However such a method has the disadvantage that, if the filtering is sufficient to achieve the desired effect (i.e., the filtering serves to block a sufficiently wide range of high-frequency components of the successively calculated values of host vehicle path probability, when there are rapid fluctuations in the yaw rate), an excessive delay may occur in the timing of selecting a preceding vehicle, and in the timing of canceling a currently established selection.